It is recognized that planar recording heads, having coils formed generally parallel to a recording media, exhibit performance improvements in comparison to heads in which the coils are mounted perpendicular to the recording medium. For example, the higher field gradients produced during a reading operation by a perpendicular head results in a distortion of the detected bit recorded on the recording medium. This distortion appears as negative signals on the leading and trailing edges of the main positive signal, or undershoot components. These undershoot signals distort the detected main signal and degrade a measured signal-to-noise ratio. Undershoot components are avoided with planar heads.
Furthermore, conventional thin film heads with vertical coils require very small throat height tolerances to maintain satisfactory output, while planar heads are less sensitive to throat height tolerance. Also, planar heads have lower normalized inductance than heads with vertical coils, which improves the signal-to-noise ratio.
A prior art planar head 1 is shown in FIG. 1. A planar top yoke 2 and insulator layer 3 are formed on a substrate 4. Magnetic return studs 5, preferably made of Permalloy (approximately 80Ni:20Fe), are formed in contact with the yoke 2 and sequential process steps form coils 6 and additional insulator layers 7. Bottom yoke pieces 8 are formed in contact with the tops of the return studs 5. Finally poles 9 are formed between the bottom yoke pieces 8, forming a gap 10. When an electric current is directed to the coils 6 by leads (not shown), a magnetic flux is generated in the top yoke 2, return studs 5, bottom yoke pieces 8 and poles 9. The flux impinges on a magnetic medium 11 to record data pulses and the data signals are read by sensing the flux emanating from the medium. For this reason, the yoke portions of magnetic head are sometimes referred to as magnetic flux guides.
Such prior art planar recording heads exhibit, however, certain performance disadvantages. For example, the return studs 5 formed of many layers display low magnetic permeability which reduces the magnetic efficiency of the head, resulting in reduced signal amplitudes. Further, the studs 5 have a magnetic anisotropy that is parallel to the substrate, which direction is perpendicular to the direction of the flux induced in the studs during writing and reading. This perpendicular orientation of the stud anisotropy with the induced flux undesirably results in noise and low efficiency of the head. The process to make conventional planar heads also includes many plating steps, e.g., with Permalloy, which makes the process difficult to control.